The present invention relates to an ethylene removal agent having an excellent activity of adsorbing and decomposing ethylene present in air or other atmospheres and a postharvest preservation agent which can be utilized to maintain the freshness of postharvest vegetables, fruits and flowers by mainly removing ethylene evolved from them.
Besides, the present invention relates to a deodorant which adsorbs and decomposes foul-smelling substances and is broadly utilized for deodorizing garbages, refrigerators, toilets, hospitals, hotels, ranches, sewage disposing plants, etc.
(A) As plants are still alive after being harvested, various physiological effects such as respiration effect, transpiration effect, mold growth and putrefaction under the action of microorganisms, etc. may take place together and accelerate the loss of freshness of the plants. In addition, plants evolve ethylene, a kind of plant hormone, as a metabolite. Ethylene has many physiological effects, among which there are respiratory promoting effect and maturity promoting effect, and, therefore, largely relates to maturity and also loss of freshness of the plants. The loss of freshness has been a problem especially in the storage or the distribution of vegetables, fruits and flowers. As the postharvest preservation to maintain freshness of vegetables, fruits and flowers, the following two methods are currently employed.
(1) A method of depressing the above physiological effects by controlling the storage conditions to low temperature, reduced pressure, low oxygen concentration, etc.
(2) A method of removing the evolved ethylene by an adsorbent or a catalyst.
Of the above two methods, the method (1) cannot be said to be easily accessible from the viewpoint that it requires special and complicated devices. In the method (2), the use of an adsorbent such as active carbon, zeolite, etc. to adsorb and remove ethylene has been proposed. Such adsorbents, however, have the defects that (1) the amount of adsorption is limited due to the saturated amount of adsorption, that (2) the adsorption ability is decreased with time on use and that (3) the once adsorbed ethylene is concentrated on the surface of the adsorbent and desorbed from the surface.
Accordingly, alternate methods have been proposed, wherein catalyst component or reactive species such as potassium permanganate, potassium bromate, etc. are carried on the adsorbent to convert adsorbed ethylene to other species. However, the thus treated adsorbents have not sufficient activity at ordinary conditions of use. It cannot be said that the defect of the adsorbent has been improved.
Other methods of utilizing oxidation activity of gaseous chlorine dioxide have been proposed. For instance, in Japanese Patent Publication No. 48-32079 (1973), a method has been disclosed wherein an aqueous solution of a chlorite is adsorbed on a basic adsorbent and stabilized, and the thus treated adsorbent is mixed with an acidic powder to generate gaseous chlorine dioxide. Furthermore, in Japanese Patent Application Laid-Open (KOKAI) No. 59-39243 (1984), a composition which is able to generate gaseous chlorine dioxide has been disclosed, wherein it is prepared by impregnating a porous inorganic carrier with an aqueous solution of a chlorite adjusted to pH 9 to 14.
However, the method of using gaseous chlorine dioxide may not be practical, because it is difficult to control the amount of generation of the gas and also to prevent its decomposition during the storage of itself. Moreover, the activity no more exists when all chlorite on the carrier is decomposed. Besides, there are some cases where the generation of chlorine dioxide is undesirable in consideration of the environmental pollution.
In addition to these, even if ethylene can be removed by the use of above ethylene removal agents, sufficient postharvest preservation will not be expected. It is difficult for them to inhibit the growth of mold and putrefaction
In the present invention, it is intended to provide a novel ethylene removal agent and a postharvest preservation agent which have not the above defects in the conventional methods.
(B) There are many varieties of sources of the generation of offensive odors, such as garbages in daily life, refrigerators, factories, ranches, sewage disposing plants, etc. Besides, there are many places having odor not offensive but characteristic, such as hospitals, hotels, restaurants, etc.
As the substances which cause these offensive odors, ammonia, mercaptans, sulfides, amines, aldehydes, etc. have attracted the attention. However, the actual situation is more complicated and the causes of offensive odors are not limited to the above substancs.
In recent years, many researches for removing the offensive odors have been performed with the raise of the demand for the methods of removing these offensive odors. Typical methods now available are summarized as follows.
(1) The masking method by using aromatic substances of pleasant smell to mask that of foul-smelling substances.
(2) The adsorption method of adsorbing the foul-smelling substances by using adsorbents such as active carbon.
(3) The acid-base neutralization method of neutralizing the foul-smelling substances with acids or bases.
(4) The chemical oxidation or reduction method of chemically decomposing the foul-smelling substances.
However, each method listed above has serious defects. The masking method cannot be said to be a substantial method. The adsorption method has a limit of the amount of adsorption due to the saturated amount of adsorption and is not effective against strong offensive odors. The acid-base neutralization method is limited to the substances which can be neutralized and, therefore the odors which can be removed are limited.
The chemical oxidation-reduction method is considered to be the most expected technique, though any method having a sufficient activity has not yet been found. Of the chemical oxidation-reduction methods, several techniques of utilizing the oxidation activity of gaseous chlorine dioxide have been proposed. For instance, in Japanese Patent Publication No. 48-32079 (1973), a method has been disclosed, wherein an aqueous solution of a chlorite is adsorbed to a basic adsorbent and stabilized, and the thus treated adsorbent is mixed with an acidic powder to generate gaseous chlorine dioxide. Furthermore, in Japanese Patent Application Laid-Open (KOKAI) No. 60-161307 (1985), a composition which is able to generate gaseous chlorine dioxide has been disclosed, wherein it is prepared by impregnating a porous inorganic carrier with an aqueous solution of a chlorite. However, the method of using gaseous chlorine dioxide is not practical, because it is difficult to control the amount of generation of the gas and also to prevent its decomposition during the storage of itself. Moreover, the activity no more exists when all chlorite on the carrier is decomposed. Besides, there are some cases where the generation of chlorine dioxide is undesirable in consideration of the environmental pollution.
Although each of the above methods has a deodorizing effect to some extent and is actually applied, the technical improvement of the methods has been strongly demanded from the view point of the above defects.
(C) In consideration of these background, the present inventors have investigated a highly active and stable ethylene removal agent which adsorbs and decomposes ethylene and a postharvest preservation agent which maintain freshness of vegetables, fruits and flowers and have also investigated a highly active deodorant which adsorbs and decomposes various kinds of bad odors of garbages, refrigerators, toilets, ranches, refuse disposing plants, sewage disposing plants, etc.
As a result of the investigation, the present inventors have found that a composition prepared by adding a specified compound to at least one compound selected from the group consisting of phosphoric acid, phosphorous acid, hypophosphorous acid, hypochlorous acid and the salts of these acids has a high activity of decomposing ethylene and foul-smelling substances and the composition can be used as a stable and active ethylene removal agent, a postharvest preservation agent and a deodorant which have not been hitherto known, and on the basis of these findings, the present inventors have accomplished the present invention.